Objective: Antigenic similarities between Mycobacterium bovis (BCG) and some tumor antigens have been observed. Similar studies are planned to compare antigens from other microorganisms and tumor lines and to test the possible biological significance of such antigen sharing. Approach: Antigenic components isolated from microorganisms and methods to measure primary interactions between them and antibodies in sera from humans, rabbits, guinea pigs, and mice will be employed to measure antibodies in sera obtained under a variety of circumstances. Since components derived from BCG showed anti-tumor properties, components of other bacteria will be similarly evaluated.